Experimental study of Interfacial and Sub-Interfacial Quasistatic Crack Growth

双材料和多相材料系统失效机制的研究是由金属、陶瓷和聚合物复合材料制成的多相组件的工业重要性所推动的。从先进的复合材料飞机结构到电子设备的包装，这些系统的失效模式的理解与应用有关。这种系统的失效可能是由于多种机制造成的：脆性基体的宏观和微观开裂，不同材料之间的界面开裂，分层等等，这取决于材料系统的具体情况。在美国国家科学基金会先前的研究资助下，PI的研究小组开发了一种紧凑的偏光/剪切干涉仪（PSI），可以用作偏光或剪切干涉仪。这种单一装置允许人们从光学各向异性材料（如Homolite和环氧树脂）以及基本上光学各向同性材料（如PMMA和玻璃）中获得应力状态。结合光学各向同性和各向异性模型材料可以提供的材料失配参数范围基本上跨越了在技术上重要的双材料系统中通常获得的范围，因此模型材料组合的结果具有广泛的适用性。从静态载荷双材料系统中获得了裂纹起裂的直接光学数据。在本工作中，将获得准静态传播界面和亚界面裂纹周围应力状态的全场光学干涉信息。先前开发的用于监测裂纹起裂的光学干涉仪将在本研究中与相对高速的录像机（6000帧/见）一起使用，以监测准静态传播。在视频记录光学数据的同时，还将使用安装在加载装置上的称重传感器和线性变化位移传感器记录负载和负载点位移数据，这些数据将用于解释实验数据的数值建模。将进行双材料和多层夹层试样的一系列实验。特别感兴趣的现象是：*界面裂纹扩展机制，其中裂纹完全在两种不同材料之间的界面上扩展；*裂纹扭结机制，裂纹从界面开始，但扭结到韧性较低的材料；*裂纹从界面扭结并在韧性较低的材料中继续扩展后的亚界面裂纹扩展状态；*夹心层中的裂缝隧道机制。收集到的数据和进行的分析，除了证实目前对界面裂纹起裂和裂纹平行问题的认识之外，还应该为我们提供更多的信息，以更好地理解裂纹扭结和裂纹隧道现象。

Study of failure mechanisms in bimaterial and multiphase material systems is motivated by the industrial importance of multiphase components made from metals, ceramics and polymer composite materials. An understanding of failure modes in these systems is relevant in applications ranging from advanced composite aircraft structures to packaging of electronic devices. Failure in such systems can be due to a variety of mechanisms: macro- and microcracking of a brittle matrix, cracking along interfaces between dissimilar materials, delaminations and so on depending on the specifics of the material system. Under a prior research grant from the NSF, the PI's research group has developed a compact Polariscope/Shearing Interferometer (PSI) that can be used as either a polariscope or a shearing interferometer. This single device allows one to obtain stress states from optically anisotropic materials (such as Homolite and epoxy) as well as essentially optically isotropic materials (such as PMMA and glass). The range of material mismatch parameters that can be provided by combining optically isotropic and anisotropic model materials essentially spans the range that is typically obtained in technologically important bimaterial systems, consequently results from the model material combinations have wide ranging applicability. Direct optical data regarding crack initiation from statically-loaded bimaterial systems have been obtained. In this work, full-field optical interferometric information will be obtained about the stress state around quasi-statically propagating interfacial and sub-interfacial cracks. The optical interferometers previously developed for monitoring crack initiation will be used in this study in conjunction with a relatively high-speed video recorder (6000 frames/see) to monitor quasi-static propagation. Simultaneous with the video recording of the optical data, load and load-point displacement data will also be recorded using a load cell and a linearly-varying displacement transducer mounted on the loading device, and these will be used in numerical modeling that can be of use in interpreting the experimental data. A series of experiments on bimaterial and multilayer sandwich specimens will be conducted. Phenomena of particular interest are: * the interfacial crack propagation regime where the crack propagates entirely on the interface between two dissimilar materials; * the crack kinking regime where the crack starts from the interface but kinks into the material with lower toughness; * the sub-interfacial crack propagation regime after the crack kinks from the interface and continues in the material with lower toughness; * the crack tunneling mechanisms in sandwiched layers. The data gathered, and the analysis performed, should provide us with additional information to gain a better understanding of crack kinking and crack tunneling phenomena, in addition to substantiating the current state of knowledge of issues of interfacial crack initiation and crack paralleling.